In conventional mobile communication systems, communication services have been provided by wireless base station devices (hereinafter also referred to as macro base stations or eNBs (e NodeBs)) each forming a cell having a radius ranging from several hundreds of meters to several tens of kilometers, i.e., an area in which wireless terminal devices are allowed to communicate with the wireless base station device.
In recent years, with a dramatic increase in the number of subscribers of mobile communication services and an increase in communication traffic due to data communication, it is desired to distribute the subscribers and the communication traffic over cells having smaller radii, and to reliably provide users with a certain level of communication speed. Further, as a countermeasure against blind zones caused by skyscrapers, it is desired to install wireless base station devices in office floors and ordinary houses.
In association with these requirements, downsizing of wireless base station devices has progressed by remarkable improvement in throughput of various devices used in the wireless base station devices, and downsized base stations have attracted attention.
Such downsized base stations (hereinafter also referred to as femto base stations or HeNBs (Home e NodeBs)) form femto cells, and each femto cell has a radius as small as about 10 meters. Therefore, it is considered that the femto base stations are used in places outside macro cells formed by macro base stations, or places where it is difficult to install macro base stations, such as homes, underground malls, and the like.
As a function for a wireless terminal device (hereinafter also referred to as a UE (User Equipment)) to access a terminal device provided in a LAN (Local Area Network) via a HeNB, LIPA (Local IP Access) is defined in 3GPP (Third Generation Partnership Project).
The LIPA is a function that enables a UE to access a LAN by using not a global IP (Internet Protocol) address assigned by a mobile communications carrier network but a local IP address for accessing the LAN.
For example, Non-Patent Literature 1 (3GPP SPEC 23.829 V1.3.0 2010.9) discloses a local gateway device (hereinafter also referred to as an L-GW). When a UE accesses a terminal device in a LAN via a HeNB, the L-GW gives a local IP address to the UE, and performs a data relaying process or the like.
The LIPA is used, for example, when a user downloads a video file from a hard disk recorder in a home LAN onto a cellular phone to watch a program.